Scavenging for two-stroke internal combustion engines



Sept. 15, 1931. T. v. HEMMINGSEN' 1,323,399

SCAVENG'ING FOR TWO-STROKE INTERNAL COMBUSTION Filed Oct. 8. 1928 Patented Sept; 15, .1931

UNITED STA TORKILD VALDEMAB HEMMINGSEN, OF COPENHAGEN, DENMARK SCAVENGING FOR TWO-STROKE INTERNAL COMBUSTION ENGINES Application filed October 8, 1928, Serial No.

This invention relates to an arrangement of scavenging applicable in both single-acting and double-acting two-stroke cycle internal combustion engines. The arrangea ment is of that kind in which scavenging takes place through ports or the like. openings. Internal combustion engines with scavenging through ports have the drawback that it is diflicult to keep those parts of the cylinder close to the exhaust ports well oiled, these parts being intensely heated by the passing exhaust gases, so that the oil becomes thin and is easily carried away with the exhaust gases. This is objectionable cspecially because the main part of the piston passes the part in question of the cylinder with the greatest speed. The importance of this drawback is highly increased when the scavenging is defective, because the said parts of the cylinder are then especially intensely heated. According to theinvention the said drawback is avoided thereby that the scavenging ports of the cylinder are controlled by a power piston, while the exhaust ports are controlled by one or more special controlling pistons having an essentially lower speed than the power piston, and besides the scavenging ports are so shaped that their directions are tangents to a cylindrical surface placed within the cylinder walland coaxial therewith. Hereby it is made possible to make the speed of the power piston as great as it might be found practical, which means that a certain output may be obtained by smaller dimensions of the engine. By shaping the scavenging ports in the above mentioned manner it is obtained in a known .manner that the scavenging air gets a rotating motion at its admission and moves up 4 through the cylinder in a helical current. Hereby is obtained a very efiicient scavenging, the combustion gases being practically fully exhausted from the cylinder in each working period, and the cylinder is filled with pure scavenging air. This means that the walls of the engine cylinder are permanently kept at a comparatively low temperature, the fresh air being able to bring its cooling power to hear at a very high degree,

and it is obtained that the bounding of the 311,204, and in Denmark October. 28, 1927.

piston speed caused by a deficient cooling is avoided. The

invention consists in the combination of the said arrangements and may be characterized mainly thereby that the scavenging ports form tangents to a cylindric surface located within the inner wall of the engine cylinder and coaxial therewith, and that they are controlled by the power piston,

whereby the exhaust ports are situated at the other end of the cylinder and are controlled by one or pistons, the speed more special controlling of which is essentially smaller than that of the power piston. The diameter of the controlling piston or pistons may, according to with that ofthe working piston or materially from this diameter.

the invention be identical may difler Preferably it is made substantially smaller in diameter. The controlling piston or pistons may ,in certain cases be provided with a bored hole,

through which the piston passes, the fit tightly on the packing rings, piston rings or ed, for instance, in

ing a certain piston rod of the working said bore being made to piston rod by means of the like mountside the bore and possessamount of tension, so as to make them exert pressure on the piston rod. The controlling piston or pistons are connected by suitable link rods more secondary sh of the engine, dir

or the like with one or afts or to the main shaft ectly or indirectly. The

motion of the controlling piston or pistons .is preferably parallel to the direction of motion of the working piston, but the arrangement may also be such that the axes of the controlling pistons are situated at suitable angles to The motion of the tons proceeds with the working piston the axis of the working piston.

controlling piston or pisthe same cycle as that of but in a reverse or nearly reversedire'ction in relation to thedirection of the latter, as

the motion of the controlling piston is preferably displaced by a suitable,

small angle in adv working piston in ance of the motion of the such a manner that the exhaust ports are uncoveredbefore the scavenging air ports at the beginning of the scavenging period, while at the end of this period the exhaust ports are covered before the scavenging air ports.

Thus it becomes possible tons, and exhaust 6 may move. m piston 6 is governed by a secondary or 1nterrod 22.

at the close of the scavenging period to have a pressure higher than ,atmospheric in the cylinder, namely a pressure corresponding to the scavenging pressure, which will serve to increase the output of the cylinder (supercharge). The cylinder cover or covers of the egnlne may be provided with. a special cylinder for the controlling piston or pisports may then be arranged in this special cylinder. In double-acting engines it may be suflicienh instead of having a controlling piston or a set of such pistons in each end of the cylinder, to let the bottom end of the cylinder be served by one or more controlling pistons, the exhaust port or ports in the top end of the cylinder being then controlled bv valves or the like. If controlling pistons are employed to serve both ends of the cylinder, "these two pistons or sets of pistonsmay be connected bysuitable mechanisms so as to make them move to time, that is, in the same cycle, while the motion of any of the two pistons or groups of pistons may otherwise proceed in accordance with its individual law of motion. The said two pistons or groups of pistons may also, however, be rigidly connected with each other, for instance by means of a crosshcad beam and rod connection, so that their motions coincide. maybe provide with one or more injecting nozzles through which fuel is admitted to the cylinder in directions either entirely or partly following the whirling motion of the scavenging air or being entirely or partly opposite to this latter motion. The invention is illustrated in the drawings, in which Fig. 1 shows a longitudinal sectional view of a constructional form of the arrangement according to the invention, Figs. 2 and 3 show sectional views of the arrangement shown in Fig. 1, on lines B-B and AA respectively, Figs. 4 and 5 show sectional views of two modified constructional forms of the invention, and Fig. 6 shows-a diagrammatical view of a link'rod connection between the main crank shaft" and two secondary or intermediary shafts connected with the controlling piston or pistons. In the arrangement for scavenging shown in Figs. 1 2 and 3 for single-acting engines, the reference character 1 indicates the cylinder, 2 the scavenging air ports, 3 the exhaust ports and 4 the working piston. The exhaust ports 3 are arranged in the cylinder cover 18 which has a cylindrical bore 19, through which the controlling piston The motion of the controlling mediaryshaft not shown) by means of a link piece 20, a lever or rocker 21 and a link Surrounding the exhaust ports 3 an annular space 23 is provided through which the combustion products are led to a flange 24 con nec ting the exhaust pipe 25 indicates the connecting red by means of The cylinder or cylinder cover which the motion of the working piston 4 shown) The latter and the secondary shaft controlling the motion of the auxiliary piston 6 are mutually positively connected in such a way that the two pistons 4 and 6 operate in the same cycle, but chiefly in opposite directions. The exhaust ports 3 are prefer ably uncovered a scavenging air ports 2. As may be seen from Fig. 2 the latter ports have such tangential directions that the scavengingair when admitted obtains a helical whirling motion as indicated by the arrows in Figs. 1 and 2. Instead of being directed perpendicular to the cylinder axis, as shown on the drawings, the ports 2 may be obliquely directed so as to form suitable smallerangles with the 'cylinder axis. 40 indicates a fuel valve mounted in the cyl' nder cover 18 through which valve the fuel is injected in a direction substantially coinciding with the direction of the whirlingmotion of the air stream, as indicated in Fig. 3. In the constructional form illustrated in Fig. 4, which is intended to be used in double-acting engines, the scavenging air ports 2 are situated at the middle of the cylinder 1 and are covered and uncovered by the working piston-4 which in its dead centre positions alternately uncovers these ports by its upper and lower edges, so that scavenging is done alternately in the upper and in the lower half of the cylinder. In this constructional formthe cylinder has no controlling or distributing piston serving its upper half, but is provided with an exhaust valve 26 mounted in the centrally arranged hollow space 25 of the upper cover 18. The valve 26 is actuated from the cam shaft of the motor (not shown) through the. medium of the lever or rocker 21 and the rod 22, in such a manner that the valve is caused to remain open during the scavenging period, the valve opening near the close of the piston stroke, a very short time before the. working piston 4 uncovers the scavenging ports 2. The

'products of combustion are then expelled through the valve 26 to the exhaust pipe which is connected by means of the connecting piece 24. At its bottom end the cylinder 1 is provided with an annular cover 27 with a circular aperture the purpose of receiving a cylinder 30 provided with exhaust ports 3'. The controlling or distributing piston 14 reciprocates within the cylinder-30, its motion being effected from the main shaft or a secondary shaft by means of a crosshead beam 11 and rods 12. The controlling or distributing piston 14 is provided with hollow internal spaces for cooling fluid and has a centrally drilled hole 7, through which the piston rod 5 of the working piston passes. The bore 7 is provided with a number of piston rings 8. inserted in annular grooves, the said piston short time prior to the 28 and a flat face 29 for.

a rotating motion. stricterl so as identical, their to Fig. 4. The link products of combustion are expelled through the ports 3 uncovered by the distributing piston 14, the said'ports being surrounded by an annular chamber 31 connected to the exhaust pipe at the flange 32-. The constructional form illustrated in Fig. 5 is'similarly intended for use in double-acting engines, and the scavenging airports 2 at the middle of the cylinder are covered and uncovered by the working piston 4. The cylinder 1 has an upper cover 18 on which is mounted a cylinder 19in which the distributing or con trolling piston 6, controlling the exhaust ports 3, reciprocates. The cylinder 1 has further a bottom cover 27 with a cylinder 30 and a controlling or distributing piston 14 controlling the exhaust ports 3' in a way similar to that described in connection with Fig. 4. The two distributing pistons 6 and 14 are interconnected by means of crosshead beams 11 and 16 and rods 15, so that the motions of the two distributing pistons are motion being essentially opposite that of the working piston 4 and of the same cycle. To the bottom ends of the rods 15 are secured crossheads 35 reciprocating in guides 36 mounted on the engine frame. By means of the'connecting rods 37 the motion is transferred to the crank shafts 38 which are connected with the main crank shaft in any suitable manner, for instance by means of gear wheels, chain drive or the link rod mechanism illustrated in Fig. 6. In this constructional form scavenging is effected in a way similar to that described with regard mechanism illustrated in Fig. 6 connecting the secondary shafts 38 shown in Fig. 5 with the main shaft 39consists of two congruent triangles a, .b, 0 and (1 b 0 each comprising three linkably connected rods whose ends are rotatably con-- nected with two sets of crankson the three shafts. This link rod device makes it pos-' sible in a very simple manner to transmit considerable quantities of work between the two secondary shafts 39. When the scavenging arrangements according to Figs. 4 and 5 are employed provision is made-similarly to what has been described in connection with Fig. 1that the scavenging air obtains a whirling motion during admission by a suitable shaping of justas provision the scavenging air ports,

may be made, ifdesired, for the fuel being introduced into the engine cylinder in directions following the rotating motion of scavenging air,

'Theinvention is not reto comprise onlythe constructional forms here'described and set forth as 38 and the main shaft the or in directions opposite thisthe various details of construction may be performed or combined For instance, similar rods as the rods 12 shown in Fig.4 may be used in the constructional form according toFig. 5 for transferring the motion of the pistons 6 and 14 direct to the main shaft. Similarly in the construc-' tional forms according to Figs. 1 to 4 the in any other way. a

arrangement of two crank shafts 38 or the like may be made use of, as described in connection with Fig. 5.

An increasement of the effect obtained by the above mentioned devices is constituted by the effect, which is obtained by the special 80 arrangements appearing from Figs. 1 and 5, viz., that the exhaust ports 3 are made essentially smaller than the scavenging air ports 2, and according to the invention even so small, that the exhaust current, due to the small size of the passage area of the exhaust ports, isthrottled without the employment of special throttlin means.

Hereby throttling is obtained in a simple and cheap manner, which throttling as known causes an increasement of the pressure in the cylinder during the last part of the scavenging period, so that the cylinder at the beginning of the compression period will contain a greater quantity of air than normally, which means an increased output of the cylinder.

I claim:

1. In a two-stroke internal combustion engine, the combination of a cylinder having a plurality of scavenging and exhaust ports therein, a power piston in said cylinder, said scavenging ports being directed tangentially to a cylindrical surface disposed within the inner wall of the cylinder and arranged coaxially therewith and controlled by said power piston, said exhaust portsbeing disposed in the end of said cylinder opposite the end containing said scavenging ports, and a second piston havin a velocity which is less than the velocity of said power piston for controlling said exhaust ports, said diameter of the piston controlling the exhaust ports being less than the diameter of the power piston. v

2.1 In a two-stroke internal combustion'engine, the combination of a cylinder having a.- plurality of scavenging and exhaust ports therein, a power piston in said cylinder, said scavenging ports being directed tangential ly to a cylindrical surface disposed within the inner wallof the cylinder and arranged .coaxially therewith and controlled by. said power piston, said exhaust ports being disposed in the end of said cylinder opposite the end containing said scavenging ports, and a second piston for controlling said exhaust ports having a bore therein through which the piston rod of the power piston extends.

3. In a two-stroke internal combustion en-' ti l scavenging ports therein, said scavenging ports being directed tangentially to a cylindrical surface disposed within the inner wall of said cylinder and arranged coaxially therewith, a cylinder cover on said cylinder, a secondcylinder arranged in said cylinder cover having a plurality of exhaust ports therein, a power piston in said first cylinder, 2 second piston in said second cylinder, said scavenging ports being controlled by a power piston and said exhaust ports being controlledby said second piston.

, 4. In a double acting two-stroke internal combustion engine, thecombination of a main cylinder having a plurality of scavenging ports therein, being directed tangentially to a cylindrical surface disposed within the inner Wall of said cylinderand arranged coaxially therewith, an upper cover on said cylinder, a second cylinder arranged in said cover and having exhaust ports therein a lower cover on said cylinder a third cylinder arranged in said lower cover and having exhaust ports therein, pistons in each of said cylinders in said covers for controlling said exhaust ports, a power piston in said main cylinder adapted to control said scavenging ports, and means interconnecting said pistons in said cylinder covers whereby the motion of said pistons are identical.

5. In a double acting two-stroke internal combustion engine, the combination of a cylinder having scavenging ports therein, being directed tangentially to a cylindrical surface disposed within the inner wall of said cylinder and arranged coaxially therewith, a cover on the lower extremity of said cylinder, a second cylinder arranged in said cover having exhaust ports therein, a working piston in said main cylinder, a second piston in said secondcylinder, said main-cylinder having exhaust ports in the upper part thereof, and valves for controlling said exhaust ports.

6. In a double-acting two-stroke internal combustion engine, the combination of amain cylinder having a plurality of scavenging ports therein, being directed tangentially to a cylindrical surface disposed within the inner wall of said cylinder and arranged coaxially therewith, an upper cover on said cylinder. a second cylinder arranged in said cover and having exhaust ports therein, a lower cover on said cylinder, a third cylinder arranged in said lower cover and having exhaust'ports therein, pistons in each of said cylinders in said covers for. controlling said exhaust ports, a-power piston in said main cylinder adapted to control said scavenging ports, means interconnecting said pistons in said cylinder covers whereby the motion of said pistons are identical, crank shafts connected to each of said pistons in said cylinder covers, a main crank shaft connected to said powerpiston, and a congruent triangular link system interconnecting said secondary crank shafts and said main crank shaft.

7. In a two-stroke internal combustion engine, the combination of a cylinder having a plurality of scavenging and exhaust ports therein, a power piston in said cylinder, said scavenging ports being directed tangentially toa cylindrical surface disposed within the inner wall of the cylinder and arranged coaxially therewith and controlled by said power piston, said exhaust ports being disposed in the end of said cylinder opposite the end containing said scavenging ports, and a second piston having a velocity which is less than the velocity of said power piston for controlling said exhaust ports, said diameter of the piston controlling the exhaust ports being less than the diameter the passage area of said exhaust ports being smaller than the passage area of the scavenging ports.

8. In a two-stroke internal combustion engine the combination as set forth in claim 1, in which the axis of the power piston and of the second piston are parallel.

9. In a two-stroke internal combustion engine the combination as set forth in claim 1,

in which the axis of the power piston and of the second piston lie in the same line.

10. In a two-stroke internal combustion engine the combination as set forth in claim 1, in which the piston controlling the exhaust ports moves in a cylinder which is connected with the cylinder of the a wall having a curved inner surface.

11. 'In a two-stroke internal combustion engine the combination as set forth in claim 3, inwhich the part of the cover connecting the cylinders of the power piston and the secpnd piston is shaped with a curved inner'surace.

In testimony whereof I aflix my signature.

TORKILD VALDEMAR HEMMINGSEN.

of the power piston,

power piston through 

